Bad.
Notice how veteran BJJ guys often have bent fingers, or how boxers have problems with their hand and wrist flexibility.
I have trigger finger in my left pinky from boxing, and have sprained plenty of wrists and fingers. A lot of hand injuries comes from punching with bad technique, but what people forget is that when you're throwing hundreds upon thousands of punches a years, you're going to throw the odd punch that doesn't land well. Especially in sparring. I'm a guitar player as well and I have to be pretty cautious with how I train now of days because of how easy hand injuries can happen.